Optical pressure monitoring system

ABSTRACT

An optical pressure monitoring system includes a tube from an infusion set and an optical signal sensor disposed to detect changes in the diameter of the tube and thereby determine pressure changes within the tube. By selecting the position of the tube relative to the optical signal emitter and optical signal receiver, the optical signal sensor can both detect pressure changes and provide an integrity check for both the functioning of the optical signal sensor and the placement of the tube. By modifying the tube to exaggerate changes in tube diameter responsive to pressure changes, the sensitivity of the optical signal sensor can be increased.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to systems for feeding solutions topatients. More particularly, the present invention relates to a systemand method for monitoring fluid pressures to ensure that the solution isproperly fed to the patient by the enteral feeding pump or similardevice. Specifically, the invention relates to the use of opticalpressure sensors to monitor fluid pressures and the presence ofocclusions in the delivery set which may interfere with solution flow tothe patient, and so that operation of the enteral feeding pump may bemodified to compensate for the pressure and/or occlusion and therebyprovide highly accurate solution delivery.

[0003] 2. State of the Art

[0004] There are numerous situations in which a solution must be fed toa patient over a period of time. In some situations, the solution isprovided directly into the blood stream of the patient. Saline solutionsand medications supplied in such a manner are typically referred to asparenteral solutions. Because parenteral solutions are often necessaryto hydrate the patient, or supply needed medications, occlusion of theinfusion delivery set can be particularly dangerous to the patient.Thus, it is important to ensure that occlusions are not impedingsolution flow. However, parenteral solutions typically have a very lowviscosity in order to faciliate absorption into the blood stream.Therefore, the risk of occlusion of the infusion set is relatively smallso long as the tube is not pinched shut by folding or some otherexternal application of force.

[0005] In contrast to a parenteral system, an enteral feeding system isused to provide nutrient solutions to patients who, for one reason or another, are unable to eat for themselves. Such a system typicallyincludes a pump which is attached to an input tube connected to a supplycontainer and to an output tube which is connected to a patient. Thepump draws nutrient solution from the supply container and delivers thesolution to the patient. By adjusting the number of rotations of themotor, or the frequency of rotations, in the pump, an enteral feedingpump can adjust its output to deliver a predetermined amount of nutrientsolution (or even medication) at a desired rate.

[0006] A significant problem with currently available enteral feedingsystems, is that the intake and output tubes may become occluded. Unlikeparenteral solutions, enteral feeding solutions have a relatively highviscosity, as they must carry sufficient nutrition to sustain thepatient. Occlusion can occur, for example, if a fibrous substance isincluded in the enteral feeding solution and somehow combines tointerfere with flow through the tube. Occlusion can also occur if a tubeis bent sufficiently to interfere with flow therethrough, or if a rollerclamp (as is commonly used for intravenous applications) is notsufficiently opened. Because of the viscosity of the solution, theamount of kinking of the tube or other interference required tointerfere with solution flow is significantly less than that required ina parenteral infusion set.

[0007] If the intake tube becomes occluded, insufficient solution may besupplied to the pump, and thus to the patient. If the output tubebecomes occluded, the flow of solution may be blocked, or the solutionmay be suddenly delivered at unusually high pressures. Additionally,medical personnel may fail to notice that the supply container is out ofsolution, or may not properly mount the intake and/or output tubes inthe pump, thereby preventing the proper amount of solution from beingdelivered to the patient. Any of these scenarios can have tragicconsequences if allowed to continue for a prolonged period of time.

[0008] Yet another concern with enteral feeding systems is that ofviscosity of the solution and viscosity changes as a container full ofsolution is pumped to a patient. Knowing the viscosity of the fluidbeing pumped through the enteral feeding system is important becausedifferent viscosities are pumped at different rates by the enteralfeeding pump. For example, a lower quantity of a highly viscous solutionwill be pumped by a given number of rotations of the enteral feedingpump motor than will be moved by the same pump when the solution has lowviscosity. In other words, the amount of solution fed to the patient candiffer substantially depending on the solution's viscosity. Thus, unlessthe pump is able to accurately determine and compensate for viscositychanges in the solution (i.e. by increasing or decreasing the rotationsof the pump rotor in a given period of time), it is difficult to knowexactly how much of the solution has been fed to the patient.

[0009] To overcome these concerns, there is a need for a system andmethod for determining flow discrepancies due to occlusions, viscosity(including changing viscosity) and/or improper fitting of pumps andintake/output tubes so that patients will not be endangered, and so thatthe proper amount of fluid will be delivered to the patient.

[0010] U.S. Pat. No. 5,720,721 (Feb. 24, 1998), which is expresslyincorporated herein, provides a significant improvement in monitoringfor enteral feeding pumps. The invention uses two pressure sensors tomonitor viscosity and occlusions, and to enable the enteral feeding pumpto compensate for the varying amount of solution which will pass throughthe pump with each rotation of the rotor. The pressure sensors engagethe elastic tube of the infusion set and monitor changes in the strainon the infusion set by occlusions and viscosity changes. The straininformation can then be processed by the pump and adjustments made tothe number of rotations of the pump rotor to compensate. In the eventthat the occlusion is too severe to compensate by modification of therotor rotations, the pump is shut down and an alarm signal generated sothat replacement tubing may be provided.

[0011] While the pressure sensor system of U.S. Pat. No. 5,720,721 is asignificant improvement over the art, it does have limitations. Thepressure sensors described in the '721 patent are relatively expensiveand must be properly mounted in the pump. Additionally, the personloading the pump must make sure that the upstream and downstreamportions of the infusion set are properly loaded in the pump housing sothat they engage the pressure sensors in the proper manner. Failure toproperly load the infusion set can interfere with the functioning of thepressure sensors.

[0012] One manner for decreasing the costs of pressure sensors is to useoptical sensors. While there are several methods for using opticalsensors to determine the presence of occlusions, each has significantdrawbacks. Some methods only allow the mechanism to determine when thepressure exceeds a certain threshold. This is done by detecting when theexpanding tube of the infusion set engages a surface, thereby modifyingreflection or refraction of light. Other methods require complexcalculations of refraction indexes or otherwise provide relativelylimited information on small pressure changes. Additionally, somemethods can vary based on the material from which the infusion set isformed, or based on whether the tube of the infusion set is opaque ortransparent.

[0013] In addition to the above, many mechanisms for monitoring pressurewithin an infusion set lack an inherent failure detector. For example,if a sensor is configured to sense only when the expanding infusion settube engages a transparent surface, the failure to record a reflectedsignal may mean that the tube has not expanded. In certain situations,however, the lack of reflected signal could also mean that the sensorhas failed and is either not sending the signal or is not receiving thereflected signal.

[0014] Thus, there is a need for an improved optical pressure monitoringsystem and method of use. Such an optical pressure monitoring systemshould be relatively inexpensive and easy to use. It should also providehighly accurate determination of pressure changes which indicateocclusions and/or viscosity changes. Furthermore, it should enable theuse of infusion sets made from a variety of materials and without regardto whether the infusion set is formed of a tube which is transparent oropaque.

SUMMARY OF THE INVENTION

[0015] Thus, it is an object of the present invention to provide

[0016] an improved method for monitoring viscosity and/or occlusions inan infusion set.

[0017] It is another object of the present invention to provide such amethod which monitors viscosity and occlusions with an optical sensorsystem.

[0018] It is another object of the present invention to provide such amethod in which the material used to form the infusion set does notinterfere with proper pressure monitoring.

[0019] It is yet another object of the present invention to provide sucha method in which the transparency or opaqueness of the solution doesnot interfere with proper pressure monitoring.

[0020] It is still another object of the present invention to provide anoptical pressure sensor system with enhanced sensitivity.

[0021] It is still another object of the present invention to providesuch a sensor system which checks the integrity of the sensor and whichensures that the infusion set is properly loaded in the sensor system.

[0022] The various objects set forth above and other objects of theinvention are realized in specific illustrated embodiments of a opticalpressure monitoring sensor system for monitoring occlusions andviscosity. It will be appreciated that all embodiments set forth may notaccomplish all objects of the invention, but that preferred embodimentswill accomplish a number of the objects and thereby provide animprovement over the prior art discussed above.

[0023] The optical pressure monitoring system typically includes atleast one optical pressure sensor having an optical signal emitter andan optical signal receiver. (As used herein, it should be understoodthat the optical signal, emitter is intended to cover electromagneticradiation, regardless of whether it falls within the range visible tothe human eye.) The optical signal transmitter and the optical signalreceiver are generally placed on opposing sides of the tube of theinfusion set. As the tube expands and contracts due to increases ordecreases in pressure, the amount of light (or radiation) received bythe optical signal receiver increases or decreases at a knownratio—thereby indicating the pressure within the infusion set.

[0024] In accordance with another aspect of the present invention, thetube of the infusion set is positioned between the optical signalemitter and the optical signal receiver so that it will always partiallyobstruct light flow between the emitter and the receiver. In such aconfiguration, the optical sensor ensures the infusion set has beenloaded properly. If the infusion set is not properly positioned, agreater amount of light will be received by the optical signal receiver.The sensor system can then generate an alarm that the infusion set isnot properly loaded in the pump.

[0025] In accordance with another aspect of the present invention, thetube of the infusion set is positioned between the optical signalemitter and the optical signal receiver so that the tube will notcompletely occlude light from the optical signal emitter from beingreceived by the optical signal receiver when the solution within thetube is within acceptable operating ranges. In such a configuration, thesensor system is able to conduct a continuous integrity check. If theoptical signal receiver has stopped indicating receipt of light, thelack of a signal will indicate that there has been a sensor systemfailure and the sensor should be replaced. The failure may be either dueto a faulty optical signal emitter which is not emitting the opticalsignal, or a faulty optical signal receiver which is not detecting thesignal sent. Either way, the patient is promptly informed of the failureand can have the sensor replaced.

[0026] In the alternative, if the infusion set is positioned to allowcomplete occlusion of light when the pressure in the infusion setexceeds an acceptable threshold, the alarm signal can be used to signalan occlusion which must be dealt with promptly. If light is still notbeing received once the infusion set has been removed from the sensor,the patient or technician will know that the sensor is not working andmust be repaired or replaced.

[0027] Between the two extremes of receiving a full optical signal andno optical signal, the signals generated by the optical signal receiverindicate the extent to which the optical signal sent by the opticalsignal emitter have been obstructed by the tube. The enteral feedingpump, etc., can convert the measured obstruction into a determination ofthe pressure within the enteral feeding pump, and the tubing of theinfusion set expands in a known proportion to pressure increases. Thepressure calculations received can then be converted into informationregarding the presence of occlusions and the viscosity of fluid withinthe infusion set.

[0028] With the presence of occlusions and the viscosity of fluid withinthe infusion set determined, the rotations of the pump may be altered(i.e. increased or decreased) to ensure that the desired amount ofsolution is infused to the patient. If the pressures detected areoutside of acceptable ranges, the pump can be shut down and a signalgenerated indicating a need to replace the infusion set.

[0029] While the monitoring of the tube diameter described aboveprovides improvements over the prior art, it has been found that yetadditional improvements in sensitivity can be achieved. In accordancewith one aspect of the present invention, a portion of the infusion settube is made with a thin-walled portion. The thin-walled portionexaggerates tube expansion and contraction due to increases anddecreases in pressure. The exaggerated expansions and contractionsexaggerate the effect on obstruction of the light transmitted betweenthe optical signal emitter and the optical signal receiver, therebyproviding increased sensitivity to changes in the pressure within theinfusion set. The voltage change which is caused by the change in lightobstruction can, in turn, be converted into more detailed informationregarding occlusions and viscosity within the infusion set.

[0030] In accordance with another aspect of the invention, a portion ofthe infusion set is disposed within a jacket. The jacket has an openingon one side through which the tube of the infusion set is visible. Onthe opposing side of the tube of the infusion set, the jacket isgenerally solid and restricts the expansion of the tube. As the pressurein the infusion set increases, the expansion of the tube within thejacket is exaggerated at the opening in the jacket because of therestriction caused by the rest of the jacket. This exaggerated expansionincreases the sensitivity of readings obtained by the sensor, as theobstruction of light transmission between the emitter and the receiveris enhanced due to the increased movement in the tube wall.

[0031] In accordance with another aspect of the present invention thetube of the infusion set is disposed in a generally planar orientation.A portion of the tube is deflected out of the planar orientation by aprojection. The projection is typically disposed on a side of theinfusion set opposite from the portion of the wall disposed between theoptical signal emitter and the optical signal receiver. The projectioncauses an exaggeration in the expansion and/or contraction of the sideof the tube of the infusion set disposed between the optical signalemitter and the optical signal receiver, thereby rendering the sensormore sensitive to pressure changes. Further enhancements in sensitivitycan be obtained by controlling the configuration of the projection andthe manner in which the projection engages the tube of the infusion set.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of theinvention will become apparent from a consideration of the followingdetailed description presented in connection with the accompanyingdrawings in which:

[0033]FIG. 1A shows a side, fragmented view of a tube of an infusion setpassing through an optical sensor in accordance with the principles ofthe present invention;

[0034]FIG. 1B shows a side view of the infusion set tube and the opticalsensor of FIG. 1A, wherein the infusion set tube has expanded indiameter due to increased viscosity or an occlusion within the tube;

[0035]FIG. 1C shows a side view of the tube portion and optical sensorof FIG. 1A, with the tube portion being contracted in response todecreased pressure caused by an occlusion or viscosity withing theinfusion set;

[0036]FIG. 1D shows a top view of the infusion set tube and the opticalsensor of FIG. 1A;

[0037]FIG. 1E shows an end view of the optical sensor and across-sectional view of the infusion set tube shown in FIG. 1A;

[0038]FIG. 2A shows a side view of a infusion set passing through analternate embodiment of an optical sensor system in accordance with theprinciples of the present invention, in which a retaining jacket is usedalong the infusion set tube to amplify changes in tube diameterresponsive to pressure changes within the tube;

[0039]FIG. 2B shows a top view of the infusion set and optical sensorsystem of FIG. 2A;

[0040]FIG. 2C shows a side cross-sectional view of another embodiment ofthe present invention which operates on principles similar to that ofthe embodiment shown in FIGS. 2A-2B;

[0041]FIG. 3 shows a side, partial cross-sectional view of yet anotherembodiment of the present invention in which the tube of the infusionset has a thin-walled portion;

[0042]FIG. 4A shows a side view of yet another embodiment of an opticalsensor system made in accordance with the present invention and aportion of the tube of an infusion set passing therethrough;

[0043]FIG. 4B shows a bottom view of an infusion set and adapter housingin accordance with the principles of the embodiment of FIG. 4A andconfigured for placement in an enteral feeding pump;

[0044]FIG. 4C shows a cross-sectional view of FIG. 4B taken along theplane 4C-4C; and

[0045]FIG. 4D shows a cross-sectional view of a number of differentabutment members configurations in accordance with the presentinvention; and

[0046]FIG. 5 shows a perspective view of an enteral feeding pumpemploying one embodiment of an optical sensor system in accordance withthe principles of the present invention.

DETAILED DESCRIPTION

[0047] Reference will now be made to the drawings in which the variouselements of the present invention will be given numeral designations andin which the invention will be discussed so as to enable one skilled inthe art to make and use the invention. It is to be understood that thefollowing description is only exemplary of the principles of the presentinvention, and should not be viewed as narrowing the pending claims.

[0048] Referring to FIG. 1, there is shown a fragmented side view of atube 4 of an infusion set. The tube 4 is disposed so that its lowerportion 4 a is positioned between an optical signal emitter 8 and anoptical signal receiver 12. Together, the optical signal emitter 8 andthe optical signal receiver 12 form an optical sensor, generallyindicated at 16.

[0049] The tube 4 of the infusion set is formed from a generallyelastomeric material such as silicone. However, as set forth below,other materials may be used.

[0050] The tube 4 is preferably positioned so that when it is in itssmallest state, the lower portion 4 a still partially obstruct lighttransmitted between the optical signal emitter 8 and the optical signalreceiver 12. As will be discussed in detail below, having the lowerportion 4 a of the tube 4 continually obstruct light transmissionbetween the optical signal emitter 8 and the optical signal receiver 12provides an important integrity check on the system by ensuring that thetube is properly loaded in the optical sensor 16.

[0051] For a tube 4 of an infusion set which is positioned down streamof the pumping mechanism, the lower portion 4 a of the tube can bepositioned such that it is slightly occluding the light between theoptical signal emitter 8 and the optical signal receiver 12 when atambient pressure. This is because any occlusion or viscosity increasedown stream from the pump mechanism (not shown) will increase pressure,causing the tube 4 to expand and move the lower portion 4 a downwardlybetween the optical signal emitter 8 and the optical signal receiver 12.In virtually all scenarios, the portion of the tube 4 downstream fromthe pump rotor will be at least as large as its ambient state.

[0052] In contrast, a portion of the tube 4 which is positioned abovethe pump rotor will have a vacuum generated within the tube with eachrotation (or other actuation) of the pump mechanism. This vacuum isamplified by an upstream occlusion or high viscosity. Thus, a portion ofthe tube 4 positioned upstream from the pump rotor will partiallycollapse or have a reduced diameter with each rotation of the pumprotor. Thus, to keep the tube 4 in a position in which it will partiallyobstruct light between the optical signal emitter 8 and the opticalsignal receiver 12, an upstream portion of the tube will need to havethe lower portion 4 a placed more deeply into the optical signal sensor16 to ensure that the it continually obstructs light flow between theoptical signal emitter 8 and the optical signal receiver 12. Of course,because occlusions are manifest by a vacuum within the upstream portionof the tube 4, the upstream portion will rarely expand beyond itsambient state.

[0053] Positioning the tube 4 so that it is always at least partiallybetween the optical signal transmitter 8 and the optical signal receiver12 provides an important integrity check for the system. If the lowerportion 4 a of the tube 4 is not initially positioned to partiallyobstruct light, a reading by the optical signal sensor 16 that there isno light obstruction can mean two things. First, it could mean that thetube 4 is not expanding beyond some predetermined threshold to cause itto enter the optical sensor. Second, it could mean that the tube 4 ofthe infusion set was never loaded into the pump in the first place.However, by keeping the lower portion 4 a of the tube 4 of the infusionset within the optical signal sensor 16, the ambiguity of the signal canbe eliminated. If the optical signal receiver 12 detects no obstructionof light between the optical signal emitter 8 and the optical signalreceiver 12, the tube 4 has not been loaded properly.

[0054] Unfortunately, it is not uncommon for health care workers andpatients to be distracted while placing the infusion set into the pump.If the infusions set is not loaded properly, the solution may not bepumped to the patient, and the patient may be deprived of needednutrients and/or medication.

[0055] In the alternative, the patient or a health care worker may havealready opened a clamp on the infusion set which prevents flow prior toloading of the infusion set in the pump. If the infusion set has beeninserted into the catheter in the patient, but not properly loaded intothe pump, the solution may be flowing freely under the force of gravityinto the patient at a rate far in excess of that desired. For somepatients, this free-flow situation can raise serious health concerns, asthe patient's body may not be able to handle the sudden “flood” ofsolution. This is especially true if the solution is medicated.

[0056] By having the tube 4 properly positioned with the optical signalsensor 16, both the patient and the health care worker can be assuredthat the flow of solution is being controlled by the enteral feedingpump.

[0057] In addition to always keeping the lower portion 4 a of the tube 4at least partially within the optical signal sensor 16, it is alsodesirable that the tube not be positioned so that it will completelyobstruct light transmission between the optical signal emitter 8 and theoptical signal receiver 12 during normal operation. By having the tube 4positioned to always allow some light flow between the optical signalemitter 8 and the optical signal receiver 12, an integrity check on theoptical signal sensor is made each time a reading is processed. If somelight is being received by the optical signal receiver 12, then thesensor 16 must be working. If no light is being received, the opticalsignal sensor 16 has malfunctioned and an alarm is generated.

[0058] Those skilled in the art will appreciate that a virtual totalobstruction of light transmission between the optical signal emitter 8and the optical signal receiver 12 could also be used to determine whenthe infusion set has an occlusion or excessive viscosity. However, insuch a scenario, an ambiguous alarm is created which could meanexcessive pressure or a faulty sensor. In any event, if the pump detectsan occlusion, an improper loading of the tube 4 of the infusion set, ora faulty optical signal sensor 16, the pump will generate one or morealarms and provide notice of the problem. The patient or health careworker may then correct the problem and restore the solution flow to thedesired level.

[0059] Turning now to FIG. 1B, there is shown a side view of theinfusion set tube 4 positioned between the optical signal emitter 8 andthe optical signal receiver 12. Typically, the optical signal emitter 8and the optical signal receiver 12 are positioned immediately adjacentto the tube 4. Preferably, both upstream and downstream portions of thetube 4 will be disposed in optical signal sensors 16 positioned near thepump mechanism to monitor pressure changes due to occlusions andviscosity. Thus, the pump will be able to detect both upstream anddownstream occlusions and changes in viscosity which may interfere withdelivery of the predetermined amount of solution.

[0060] As shown in FIG. 1B, the optical sensor 16 is positioned on adownstream portion of the tube 4. With each rotation of the pump rotor,solution is forced down the tube 4, causing a short pressure increaseand expansion of the tube. If the viscosity of the solution changessignificantly or there is an occlusion, the amount of pressure increaseand/or its duration will change. FIG. 1B shows a tube 4′ which hasincreased in diameter due to an occlusion downstream from the sensor. Bymonitoring the extent of the increase in tube size, the effect of anyocclusions can be determined. While some partial occlusions may effectflow relatively little, an occlusion can also significantly impairsolution flow and can cause the solution to be delivered to the patientat an undesirably high pressure. Thus, if the optical sensor 16 detectsa pressure increase above a predetermined threshold, an alarm will begenerated indicating that the infusion set should be checked. If thepressure detected by the optical signal sensor 16 is so high as topresent safety concerns, the pump can be shut down until it has beenchecked.

[0061]FIG. 1C shows an upstream portion of the tube 4″ positionedbetween an optical signal emitter 8 a and an optical signal receiver 12a. Unlike the downstream portion of the tube 4′, the upstream portion ofthe tube 4″ will generally have a vacuum created therein with eachrotation of the pump rotor (or other actuating movement of the pumpmechanism). Thus, the tube 4″ in FIG. 1C is smaller in diameter than thetube 4 in FIG. 1A and much smaller in diameter than the tube 4′ in FIG.1B.

[0062] While each rotation of the rotor will cause the tube 4″ totemporarily shrink in diameter, the presence of occlusions or highviscosity can amplify the shrinking and require additional time for thetube to return to its normal diameter. If the tube has not returned toits normal diameter by the time the pump conducts its next rotation,there will be less solution in the tube for movement by the tube, andeach rotation of the pump rotor will deliver less solution than when thesolution is at normal pressure. By monitoring the upstream pressure inthe infusion set, however, the pump can increase the number or frequencyof rotations (or other actuating motion) to compensate for the pressurechanges, and thereby ensure that the proper amount of solution is beingdelivered to the patient. If the occlusion or viscosity is causing toomuch impediment to solution flow through the tube 4″, the pump cangenerate an alarm, thereby informing the user or health care worker thatthe infusion set must be checked.

[0063] As with the downstream optical signal sensor 16, the upstreamoptical signal sensor 16 a can fail. Likewise, the tube 4″ of theinfusion set can be loaded improperly. Thus, it is preferred to have thetube 4″ always obstruct some, but not all, of the light flow between theoptical signal emitter 8 a and the optical signal receiver 12 a.

[0064] Turning now to FIG. 1D, there is shown a top view of the infusionset tube 4 and the optical signal sensor 16 of FIG. 1A. In such anembodiment it is preferred that the optical signal emitter 8 and theoptical signal receiver 12 are positioned immediately adjacent the tube4 of the infusion set. While the optical signal emitter 8 and theoptical signal receiver 12 need not touch the tube 4, having the twosensors constrict radial expansion on the sides of the tube will causeincreased expansion of the tube vertically, thereby amplifying thechanges caused by pressure.

[0065]FIG. 1E shows a cross-sectional view of the tube 4 and an end viewof the optical signal emitter 8 and the optical signal receiver 12. Fromthis view, it is apparent that radial expansion of the tube 4 willinterfere with transmission of optical signals, represented by arrows18, between the optical signal emitter 8 and the optical signal receiver12. The extent to which the tube 4 interferes with the lighttransmission is proportional to the pressure changes which occur withinthe tube during operation of the pump. It is not proportional to, thereflective index of the material or whether the material is clear oropaque. Thus, a variety of materials could be used for the tube 4 ifdesired.

[0066]FIG. 2A shows a side view of a infusion set 24 passing through analternate embodiment of an optical sensor system 36 in accordance withthe principles of the present invention. Disposed along the tube 24 ofthe infusion set is a jacket 40. While the tube 24 of the infusion setis formed from a radially expandable material such as silicone, thejacket 40 is formed from a generally rigid material that will haveminimal if any radial expansion in the pressure range typicallyassociated with solution feeding systems.

[0067] In the top of the jacket 40 is an window 44. The window 44exposes a portion 24 a of the tube 24 of the infusion set. Because thejacket 40 constricts expansion of the tube 24, expansion created bychanges in the tube are amplified in the portion 24 a of the tubeadjacent the window. By having the optical signal emitter 28 and theoptical signal receiver 32 disposed on opposing sides of the window 44,the pressure changes within the infusion set can be more accuratelydetermined due to the amplification created by the jacket 40.

[0068] Turning now to FIG. 2B, there is shown a top view of the infusionset, including the tube 24 and the jacket 40. The optical signal emitter28 and the optical signal receiver 32 of the optical signal sensor 36are disposed on opposing sides of the window 44 in the jacket so as tomonitor the rise and fall of the portion 24 a of the tube 24 exposed bythe window 44.

[0069]FIG. 2C shows a cross-sectional view of an alternate embodiment ofthe present invention, which operates in substantially the same manneras the embodiment shown in FIGS. 2A and 2B. Instead of having a jacket,however, the infusion set, generally indicated at 50, has a rigid tube52 and a radially expandable tube 54. The rigid tube 52 has an openingor window 56 which is covered by a portion 54 a of the radiallyexpandable tube 54. As with the portion 24 a in FIGS. 2A and 2B, theportion 54 a tends to expand to a greater degree than the remainder ofthe tube 54 because the rigid tube 52 constricts expansion in all butone direction. Thus, placing the optical signal sensor (not shown inFIG. 2C) adjacent the portion 54 a of the tube 54 provides improvedsensitivity.

[0070] Turning now to FIG. 3, there is shown a side, partialcross-sectional view of yet another embodiment of the present invention.The infusion set 60 includes a tube 64 disposed between the opticalsignal emitter (shown in shadow 68) and the optical signal receiver(shown in shadow 72) of the optical signal sensor 76. The portion 64 aof the tube 64 disposed between the optical signal sensor 76 has athin-walled portion on one side. Preferably, the thin-wall portion isbetween 0.025 and 0.050. The outer circumference of the tube 64 and willbe between 0.175 and 0.300 thinner than the normal thickness of the tube64. As pressure within the tube 64 changes, the thin-walled portion 64 awill expand and contract to a greater extent. The exaggerated expansionand contraction provides increased sensitivity to pressure changes, asthe optical signal sensor 76 can more readily detect pressure changesdue to the exaggerated movement.

[0071] Turning now to FIG. 4A, there is shown a side view of yet anotherembodiment of an optical sensor system made in accordance with thepresent invention and a portion of the tube of an infusion set passingtherethrough. The tube 84 is disposed generally above an optical signalemitter 88 and an optical signal receiver 92 which form an opticalsignal sensor, generally indicated at 96.

[0072] The tube 84 is positioned in a generally planar configuration.However, a portion 84 a of the tube 84 positioned above the spacebetween the optical signal emitter 88 and the optical signal receiver 92is engaged by an abutment member 100 so as to deflect that portion ofthe tube into the space 104 between the optical signal emitter 88 andthe optical signal receiver 92.

[0073] The abutment member 100 serves two valuable functions. First, theabutment member 100 helps to ensure the tube 84 of the infusion set isin the desired location and helps resist movement of the tube which maybe caused by the pump mechanism. Second, the abutment member 100prevents expansion of the tube 84 along the top side thereof adjacent tothe optical signal sensor 96. This causes pressure changes to expand andcontract the opposing wall 84 b of the tube in an exaggerated manner tohow the sidewalls of the tube will normally respond to pressure changes.As with the embodiments discussed above, this exaggerated movementallows the optical signal sensor 96 to detect smaller changes inpressure, and thereby provide more accuracy in determining pressurechanges within the infusion set.

[0074] Turning now to FIG. 4B, there is shown a bottom view of the tube84 of an infusion set 86 and the abutment member 100 as used inaccordance with the principles of the present invention. In addition tothe tube 84, the infusion set includes an upstream intake tube 86 a anda downstream output tube 86 b.

[0075] The tube 84 of the infusion set has a looped portion 84 c whichwraps around the rotor (not shown) of an enteral feeding pump, orsimilar device. The abutment member 100 is disposed to engage the tube84 of the infusion set 86 both upstream and downstream from the pumprotor. As will be discussed in additional detail below, pressure ismonitored both upstream and downstream from the pump rotor to ensurethat 1) a known quantity of solution reaches the portion of the tube 84which engages the pump rotor, and 2) that the solution pumped by thepump rotor reaches the patient.

[0076] The tube 84 of the infusion set 86 is typically made from anelastomeric material such as silicone. This allows the tube 84 tostretch and to expand and contract is it is worked by the pump rotor tomove solution through the tube. The remainder of the infusion set 86,however, need not be formed from silicone. To the contrary, lessexpensive tubing can be used for the remainder of the infusion set 86.The silicone tube 84 and the remainder of the infusion set 86 aretypically held together by an adaptor 108 having two connectors 110.These connectors 110 can be formed as an integral, one piece adaptorincluding the abutment member 100, or can be formed separately.

[0077] As the pump rotor rotates, a vacuum is created in the upstreamportion 84 d of the tube 84 of the infusion set. This vacuum will causetube portion 84 b along the upstream portion 84 d to contract. Theextent of contraction and the time necessary to return to ambient is afunction of the viscosity of the solution upstream from the pump rotorand the presence of any occlusions. By monitoring the change in thediameter of the tube portion 84 b upstream from the pump rotor, theenteral feeding pump is able to determine the viscosity and occlusion'seffect on solution flow rate and thereby determine the amount ofsolution which is being pumped by each rotation of the pump rotor. Thisis typically done by monitoring the voltage produced by the opticalsignal receiver. The greater the voltage which is received, the greaterthe amount of light which is getting passed the tube portion 84 b. Ifthe monitored collapse of the tube portion 84 b indicates that theviscosity is too great or that there is an occlusion, the voltagereading will be higher than expected and the enteral feeding pump cangenerate an alarm signal indicating that a predetermined threshold hasbeen passed.

[0078] Unlike the upstream portion 84 d of the tube 84 of the infusionset 86, the downstream portion 84 e will receive increased pressure witheach rotation of the pump rotor, thereby causing the downstream portion84 b to expand. The expansion will restrict light flow from the opticalsignal emitter to the optical signal receiver, thereby decreasing thevoltage generated. If the pressure increase lasts for too long a periodof time or is too great, the optical signal sensor (not shown) willproduce voltage readings indicative of the excess or prolonged expansionof portion 84 b along the downstream portion 84 e of the tube 84. Theenteral feeding pump can then generate an alarm indicating an occlusiondownstream. This will prevent the patient from being subject to suddenpressure increases which could cause discomfort or even injury.

[0079] As mentioned with respect to FIG. 4A, the abutment member 100increases the accuracy of the optical signal sensor 96 by exaggeratingthe expansion (downstream) or contraction (upstream) along the tubeportion 84 b. This exaggerated movement enables the enteral feeding pumpto more accurately determine pressure by the voltage readings producedby the optical signal sensor.

[0080] Turning now to FIG. 4C, there is shown a cross-sectional view ofthe tube 84 of the infusion set 86, and fragmented views of the abutmentmembers 100 a and 100 b. In the upstream portion 84 d of the tube 84 ofthe infusion set 86, the monitored property is almost always contractionof the tube. To this end, it has been found preferable to have anabutment member 100 a which forms a relatively narrow projection andextends into engaging contact with the exterior of the tube 84.Preferably, the end of the projection should have a thickness (i.e. across-section taken generally coplanar with the cross-section of thetube) with a radius which is ⅛ the diameter of the tube 84. The narrowprojection formed by the abutment member 84 a allows the outer edges ofthe tube 84 to move upward and downwardly. This has been found toincrease sensitivity to the vacuum created within the upstream portion84 d of the tube 84, and thereby enables the voltage reading of theassociated optical signal sensor to more accurately indicate thepressure within the tube.

[0081] Because the downstream portion 84 e of the tube 84 generallymonitors only pressures at ambient or greater, it is not necessary forthe abutment member 100 b to form such a protrusion. Rather, theabutment member 100 b is generally broader and generally presses againstthe entire top of the tube 84 at the location adjacent the opticalsignal sensor. As the pressure in the downstream portion 84 e of thetube 84 increases, the relatively flat abutment member 100 b limitsexpansion of the tube upwardly, thereby causing exaggerated expansion onthe opposing side 84 b of the tube 84.

[0082] While a relatively narrow protrusion 100 a and a broad protrusion100 b are shown for the abutment members, those skilled in the art willappreciate that abutment members having a variety of cross-sections maybe used. For example, FIG. 4D shows the cross-section of protrusionswhich are generally squared, semi-oval and triangular. Through routineexperimentation, those skilled in the art will be able to determineappropriate voltage curves associated with the shape and the tubing tobe used.

[0083] Turning now to FIG. 5, there is shown a perspective view of anenteral feeding pump, generally indicated at 130, formed in accordancewith the principles of the present invention. The pump 130 includes amotor unit 134 with a digital readout 138 and a plurality of controlbuttons 142. The motor unit 134 controls a rotor 146, which has aplurality of rollers 150 (typically three) which are configured toengage the tube 84 of the infusion set 86.

[0084] As the rotor 146 rotates, the rollers 150 selectively pinch offthe tube 84 and push solution contained therein downstream. If nopressure changes where present, one could readily determine the amountof solution moved by the pump 130 by simply counting the rotations. Thepressures within the infusion set 86, however, effect the amount ofsolution which is moved by each rotation of the rotor 146. Bydetermining these pressures, one can quite accurately calculate theamount of fluid being pumped. Thus, it is important to track theupstream and downstream pressures in the infusion set 86.

[0085] As shown in FIG. 5, the connectors 110′ which connect the intaketube 86 a and output tube 86 b of the infusion set 86 to the tube 84 areformed integrally with an anti-free flow device 160 which is disposedwithin the tube 84 in the form of an adaptor housing 164 which nestswithin a pair of channels 168 on the enteral feeding pump 130. Thehousing may also have integrally formed therein one or more abutmentmembers similar to those discussed above. In the alternative, a cover170 which is used to hold the housing 164 to the channels 168 of theenteral feeding pump 130 may have one or more abutment members 174formed thereon. Closing the cover 170 causes the abutment member 174 toextend through an opening in the housing 164 and to engage the tube 84.The tube 84 is then automatically and properly positioned between theoptical signal emitter and the optical signal receiver (not visible inFIG. 5) which are disposed along the channels 168.

[0086] Because the abutment member 174 will push the tube 84 into aposition in which the tube partially obstructs optical signals in theoptical signal sensor, a high voltage signal from the sensor willindicate that the tube 84 of the infusion set is not properly loaded,and/or that the cover 170 has not been properly closed. A catch 178 canbe used to hold the cover 170 closed.

[0087] By using the digital display 138 or an auditory signal, theenteral feeding pump 130 can readily determine and display the amount ofsolution which is being pumped during a given amount of time. It canalso develop a signal when thresholds are exceeded, and can indicatetrends in increased or decreased viscosity if desired. Furthermore, ifthe pump has been set to deliver a predetermined amount of solution in agiven time, the enteral feeding pump 130 is able to adjust the rotorfrequency (i.e. the number of times the rotor 146 rotates in a givenamount of time)to ensure the desired amount of solution has beendelivered. Thus, the present invention is able to obtain the advantagesset forth in U.S. Pat. No. 5,720,721, without the need of using pressuretransducers or other similar, costly devices.

[0088] By utilizing the aspects of the present invention discussedabove, an optical sensor can be used to provide highly accurate pressureand viscosity information while substantially lowering the cost of theenteral feeding pump. While numerous different embodiments of thepresent invention have been disclosed, those skilled in the art willappreciate numerous modifications which can be made without departingfrom the scope and spirit of the present invention. The appended claimsare intended to cover such modifications.

What is claimed is:
 1. A method for monitoring pressure in an infusionset for administering solution to a patient, the method comprising:selecting an optical signal sensor having an optical signal emitter andan optical signal receiver; and positioning a tube of an infusion setadjacent to the optical signal sensor so that changes in the diameter ofthe tube changes an amount of optical signals detected by the opticalsignal receiver.
 2. The method according to claim 1, wherein the methodcomprises generating a voltage indicative of the obstruction of lightcaused by the tube of the infusion set and determining pressure in theinfusion set from the voltage.
 3. The method according to claim 1,wherein the method comprises positioning the tube of the infusion set sothat the tube obstructs signals sent from the optical signal emitter tothe optical signal receiver so long as the pressure within the tube ofthe infusion set does not fall below a predetermined threshold.
 4. Themethod according to claim 3, further including positioning the tube inthe optical signal sensor so that the tube always at least partiallyobstructs the transmission of optical signals from the optical signalemitter to the optical signal receiver.
 5. The method according to claim1, wherein the method comprises positioning the tube of the infusion setso that the tube does not obstruct all optical signals sent from theoptical signal emitter to the optical signal receiver so long as thepressure within the tube of the infusion set does not exceed apredetermined threshold.
 6. The method according to claim 1, wherein themethod comprises positioning the tube of the infusion set in the opticalsignal sensor so that expansion of the infusion set will not completelyobstruct the transmission of optical signals between the optical signalemitter and the optical signal receiver.
 7. The method according toclaim 1, wherein the method comprises selecting an infusion set having atube with a thin-walled portion and disposing the thin-walled portionbetween the optical emitter and the optical receiver.
 8. The methodaccording to claim 1, wherein the method comprises developing a voltagereading representing a change in side of the size of the tubing.
 9. Themethod according to claim 1, wherein the method comprises forming theinfusion set with a tube and a jacket disposed about the tube, thejacket having an opening therein.
 10. The method according to claim 9,wherein the method further comprises positioning the opening in thejacket between the optical signal emitter and the optical signalreceiver.
 11. The method according to claim 1, wherein the methodfurther comprises forming the infusion set from a piece of generallyrigid tubing having an opening along a wall thereof, and a piece offlexible tube, the flexible tube covering the opening in the rigid tube.12. The method according to claim 11, wherein the method furthercomprises positioning the opening in the rigid tube between the opticalsignal emitter and the optical signal receiver.
 13. The method accordingto claim 1, wherein the method comprises disposing the tube inengagement with an abutment member for pushing the tube between theoptical signal emitter and the optical signal receiver.
 14. The methodaccording to claim 13, wherein the method comprises pushing a portion ofthe tube engaging the abutment member downwardly into a position betweenthe optical signal emitter and optical signal receiver.
 15. The methodaccording to claim 13, wherein method comprises holding the tube of theinfusion in a plane, and positioning the abutment member to forces aportion of the infusion set out of said plane.
 16. The method accordingto claim 13, wherein the abutment member is positioned to limitexpansion of the tube in one direction and thereby cause exaggeratedexpansion of the tube in another direction.
 17. The method according toclaim 13, wherein the abutment member has an end which engages the tube,and wherein the end has a radius which is smaller than the tube.
 18. Themethod according to claim 17, wherein the tube has a radius, and whereinthe method comprises selecting an abutment having an end with a radiuswhich is ⅛th the diameter of the tube taken generally parallel to thediameter of the tube.
 19. The method according to claim 13, wherein theabutment member has a cross-section which is generally square.
 20. Themethod according to claim 13, wherein the abutment member has asemi-oval cross-section.
 21. The method according to claim 13, whereinthe abutment member has a triangular cross-section.
 22. The methodaccording to claim 1, wherein the method comprises positioning the tubeof the infusion set about a rotor of an infusion pump to divide the tubeinto an upstream portion and a drownstream portion.
 23. The methodaccording to claim 20, wherein the method further comprises using theoptical signal sensor for monitoring the extent of contraction in thediameter of the tube in the upstream portion of the tube.
 24. The methodaccording to claim 20, wherein the method further comprises using theoptical signal sensor for monitoring the extent of expansion in thediameter of the tube in the downstream portion of the tube.
 25. Themethod according to claim 22, wherein the method comprises positioningan optical signal sensor adjacent the upstream portion of the tube andan optical signal sensor adjacent the downstream portion
 26. An adapterfor disposition along an infusion set, the adaptor comprising: a firstconnector for attaching an upstream portion of an infusion set to a tubeconfigured for engaging a pump rotor; a second connector for attaching adownstream portion of an infusion set to the tube configured forengaging the pump rotor, the second connector being attached to thefirst connector; and an abutment member disposed adjacent to the firstconnector and the second connector, the abutment member being configuredfor deflecting a portion of the tube into a nonlinear position.
 27. Theadaptor according to claim 26, wherein the first connector is configuredfor receiving a tube of a known diameter at ambient pressure, andwherein the abutment member has a first portion having an end configuredfor engaging the tube, the first portion having an end having across-sectional diameter which is about ⅛th the diameter of the tube,such that the end presses inwardly into the tube when the tube isattached to the first connector.
 28. An infusion set for an enteralfeeding pump comprising the adaptor of claim 26, and further comprisingan upstream tube connected to the first adaptor, a downstream tubeconnected to the downstream adaptor, and a tube having two ends, one endbeing attached to the first connector and the other end being attachedto the second adaptor.
 29. An apparatus for infusing solution into apatient, the device comprising: an infusion pump having a rotor formoving solution through a tube; a infusion set having a tube engaged bythe rotor of the infusion pump; at least one optical signal sensordisposed along the tube, the optical sensor having an optical signalemitter and an optical signal receiver disposed on a side of the tubeopposite from the optical signal emitter, the optical signal sensorbeing configured to detect changes in the diameter of the tube.
 30. Theapparatus of claim 29, wherein the at least one optical signal sensorcomprises a first optical signal sensor disposed along the tube upstreamfrom the rotor, and a second optical signal sensor disposed along thetube downstream from the rotor.
 31. The apparatus of claim 29, furthercomprising an abutment member disposed to engage and deflect the tubeout of a planar flow-path.
 32. The apparatus of claim 31, whereininfusion set has an upstream tube and a downstream tube attached to thetube by an adaptor, and wherein the abutment member is disposed on theadaptor.
 33. The apparatus of claim 31, wherein the pump has a cover andwherein the abutment member is disposed on the cover such that closingthe cover causes the abutment member to engage the tube.
 34. Theapparatus of claim 29, further comprising a jacket having an openingtherein disposed about the tube.
 35. The apparatus of claim 34, whereinthe opening in the jacket is disposed between the optical signal emitterand the optical signal receiver.
 36. The apparatus of claim 29, whereinthe tube has a thin-walled portion, and wherein the thin-walled portionis disposed between the optical signal emitter and the optical signalreceiver.
 37. The apparatus of claim 29, wherein the tube includes arigid portion with an opening along a sidewall thereof, and a resilientportion covering said opening.
 38. The apparatus of claim 37, whereinthe opening in the rigid portion is disposed between the optical signalemitter and the optical signal receiver.
 39. An apparatus for monitoringpressure in an infusion set for administering a solution to a patient,comprising; an optical signal sensor having an optical signal emitterand an optical signal receiver; and a resilient tube positionedproximate said signal sensor, said optical signal emitter positioned topass an optical signal at least partially over a surface of said tube tobe received by said optical signal receiver.
 40. An apparatus formonitoring pressure in an infusion set for administering a solution to apatient, comprising: a housing; an elongate flexible tube positionedwithin said housing; an abutment member positioned within said housingengaging a surface of said elongate flexible tube for substantiallypreventing expansion of said elongate flexible tube in the direction ofsaid abutment member; and an optical signal sensor positioned adjacentsaid elongate flexible tube and opposite said abutment member formeasuring expansion and contraction of said elongate flexible tube.